Fluids and microbial penetration in the internal part of cement-retained versus screw-retained implant-abutment connections

Background: It has been recently observed that in implants with screw-retai ned abutments, in in vitro as well as in vivo conditions, bacteria can pene trate inside the internal cavity of the implant as a consequence of leakage at the implant-abutment interface. An alternative to screw-retained abutme nts is represented by implants that can receive cemented abutments. In this case, the abutment goes through a transmucosal friction implant extension (collar) and is cemented inside the internal hexagonal portion of the impla nt. The aim of the present research was to compare fluids and bacterial pen etration in 2 different implant systems, one with cement-retained abutments (CRA) and the other with screw-retained abutments (SRA). Methods: Twelve CRA dental implants and 12 SRA implants were used in this s tudy. The research was done in 3 steps: scanning electron microscopic (SEM) analysis, fluid penetration analysis, and bacterial penetration analysis. Results: 1) Under SEM it was possible to observe in the SRA implants a mean 2 to 7 mu gap between implant and abutment, while in the CRA implants, the gap was 7 mu. In the latter group, however, the gap was always completely filled by the fixation cement. All the spaces between abutment and implant were filled by the cement. 2) With SRA implants, it was possible to observe the presence of toluidine blue at the level of the fixture-abutment interf ace and the internal threads; the absorbent paper was stained in all cases. With CPA implants, the absorbent paper inside the hollow portion of the im plants was never stained by toluidine blue. No penetration of toluidine blu e was observed at the implant-abutment interface and inside the hollow port ion of the implants. 3) In all the SRA implant assemblies, bacterial penetr ation was observed at the implant-abutment interface. No bacteria were dete cted in the hollow portion of the CRA implants. Conclusion: On the basis of the results obtained in the present study using 2 different implant systems, we conclude that CRA implants offer better re sults relating to fluid and bacterial permeability compared to SRA implants .